Snap-acting liquid metal switch



June 27, 1967 E. K. MACKENZIE SNAP-ACTING LIQUID METAL SWITCH 3 Sheets-Sheet 1 Filed April 14, 1965 A TTOPA/E n",

June 27, 1967 E. K. MACKENZIE 3,

SNAP-ACTING LIQUID METAL SWITCH Filed April 14, 1965 3 SheetsSheet 2 A TT'OPNEY I June 1967 E. K. MACKENZIE ACTING LIQUID METAL SWITCH SNAP 3 Sheets-Sheet 5 Filed April 14, 1965 IN VENTOR. 18597 KEN/v50) MAC/(M'Z/E ,4 ITO/FIVE United States Patent 3,328,546 SNAP-ACTING LIQUID METAL SWITCH Elbert Kennedy Mackenzie, Wales, Pa., assignor to Yarway Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Apr. 14, 1965, Ser. No. 447,989 4 Claims. (Cl. 200-152) This invention relates to electrical switches and more particularly to mechanically operated liquid metal switches.

An object of this invention is to provide a liquid metal electrical switch capable of achieving and maintaining a high capacity rating.

A further object of this invention is to provide a liquid metal switch activatable wiithout the necessity of using a tilting mechanism.

An additional object of this invention is to i provide a mechanism for rapidly breaking the electrical circuit in such a switch to minimize or prevent arcing between the contacts as they are being separated or brought together.

A further purpose is to provide a light weight durable liquid metal electrical switch having stationary metal switch mountings and switch connections as opposed to tilting switch mountings and flexible switch connections in conventional liquid metal switches.

An additional object of this invention is to provide a liquid metal switch which is hermetically sealed as one 'unit, thus making it explosion and environment-proof and capable of maintaining a constant atmosphere for optimum contact life.

These and other objects of the invention can be accomplished by providing a pool of liquid metal such as mercury and snapping a solid conductor into and out of the pool by means of a snap-acting wire-in-tube torsional responsive device. Alternatively the objects are accomplished by displacing a portion of the liquid metal pool either into or out of contact with other conductors by rapidly immersing a displacement block into the pool by means of these same torsional responsive devices. Preferably, the objects of the invention are accomplished by snapping an insulating barrier into and out of a pool of liquid metal so as to electrically isolate portions of the liquid metal pool contacting one solid conductor from portions contacting another solid conductor, the solid conductors being connected by the union of the liquid metal pools.

Conventional mechanical snap switches have inherent difliculties with respect to the corrosion of contact points and the pressure exerted between them which tends to affect switch life and current carrying capacity. While conventional tilt-type liquid metal switches eliminate these problems, they have the marked disadvantage of not being able to make a fast break in a circuit because the liquid metal which forms the contact tends to draw into a narrow head when the switch is tilted between closed and open positions. Thus, before the liquid metal breaks clean from the contact or as it is just being brought into contact, the current is forced to travel through a narrow bead of liquid. Because of this a constant capacity cannot be maintained in such switches.

Tiltable mercury switches also require an external mechanism for actuation which is subject to disalignment. Mechanical snap switches are approved by the Underwriters Laboratories as individual switching units, but since the present design of mercury switches have their operational performance strongly dependent upon these separate tilting mechanisms, they cannot obtain Underwriters approval as individual switching units. Such approvals can be obtained only in conjunction with the com- Patented June 27, 1967 ice plete tilting mechanism assembly which presently is a variable for each type of application.

While mechanical switches are capable of snapping the contacts apart, the contacts are required to separate from a stationary condition and thus the maximum speed of contact separation is limited with the result that arcing tends to occur between the contacts as the current tries to continue to flow across the gap.

The electrical liquid metal switch of this invention overcomes the disadvantages of these prior art switches by providing a liquid metal pool as a contact and rapidly snapping a solid conductor or insulating barrier either into or out of the pool to make or break the circuit. The switches, in addition to eliminating the corrosion and pressure problem of mechanical switches also avoid the inherent ditficulties of mercury switches as the contacts are snapped together like a mechanical switch rather than tilting the liquid metal from one side of the switch to the other to make or break the circuit.

With the proposed construction the moving contact member or insulating barrier is started in motion by the snap-acting torsional responsive device as it remains below the surface of the liquid metal pool without interrupting the current flow. By the time the end of the contact or insulating barrier reaches the surface of the metal pool, it is travelling at such a rate of speed that a fast clean break in the circuit is achieved with a minimum of arcing occurring between the contacts. Thus, the device of the present invention not only eliminates the trailing of the bead of mercury in the liquid metal switch, but also overcomes the arcing resulting from the separation of contacts of a mechanical switch from a stationary position. Because the switches of the present invention are capable of rapidly breaking the contacts, they are capable of achieving approved high capacity ratings.

Much lower force levels are needed to operate the switches than those required in mechanical switches where it is necesasry to have considerable contact pressure between the solid contacts.

Further objects and advantages will appear in the specification and claims.

In the drawings, I have chosen to illustrate a few only of the numerous embodiments in which the invention may appear, selecting the forms shown from the standpoint of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

FIGURE 1 is a perspective view of one embodiment of the invention showing a glass enclosed unit with two pools of liquid metal contacts, the contact bar being shown in the open position.

FIGURE 2 is a perspective view of the device shown in FIGURE 1 with the contact bar in a closed position, thus completing the electrical circuit.

FIGURE 3 is a fragmentary view of the snap-acting torsional responsive device which snaps the contact bar as shown in FIGURE 1 into and out of the liquid metal pool. 7

FIGURE 4 is another embodiment of the invention showing the use of a wettable displacement block to complete the contact between two pools of liquid metal.

FIGURE 5 is a sectional view of :a single pole, single throw switch in the open position, the switch being closed by snapping the displacement block into the pool causing it to rise and join with the other thus closing the circuit.

FIGURE 6 is a sectional view of a modified form of the invention wherein the contact bar itself completes the circuit on being snapped into the pool.

FIGURE 7 shows an additional modified form wherein an annular non-wetta'ble displacement block is used to displace the liquid metal away from contact with a stationary conductor.

FIGURE 8 is a sectional view of a switch using the displacement principle causing the liquid metal to rise to complete the circuit to two stationary conductors.

FIGURE 9 is a perspective view similar to the single pole switch shown in FIGURE 1 but shows a double throw type with a common liquid metal pool.

FIGURE 10 is a sectional view similar to the switch shown in FIGURE 7 wherein a non-wettable ceramic cup is used to isolate the liquid metal in the cup contacting the stationary contact from the pool of liquid metal in the enclosure when the switch is in the open position.

FIGURE 11 is a fragmentary perspective view showing a multiple contact switch similar to that shown in FIG- URE 9.

With respect to the drawings, the snap-acting wire-intube torsional responsive device, hereinafter referred to as the tube, is more fully described in US. Patent No. 3,067,623 entitled, Transmission of Motion from Closed Space, and in patent application Ser. No. 203,352, filed June 18, 1962, entitled, Controlled Torque and Motion Device Through a Wall, now US. Patent No. 3,183,727, representing an improvement of this device.

Essentially this device consists of a flexible hollow tube having within it a wire wit-h a preformed curvature to it. The tube may also be curved but preferably, as claimed in the application, consists of a tube maintaining a straight position when relaxed. The wire when free from the tube has a prestressed curvature along that portion which is to extend into the tube. When the wire is placed inside a tube, the tube assumes a conforming curvature but of a radius greater than the radius of curvature of the wire alone, the tube and wire each being deflected from their relaxed position by reason of the residual force of each. As seen in FIGURE 3, the tube is shown free and in the relaxed position in phantom. After the curved core wire 21 is placed within the tube it assumes a curvature as shown in full. If the curved wire were free, it would assume a curvature with even :a smaller radius.

The tube is sealed at its outer end with the curved Wire running free therein and this represents the switch mechanism. When the tube is deflected from its relaxed position, the outer tube is thus forced to assume a different curvature. This creates a force on the prestressed curved inner wire causing it to whip or snap around within the tube to assume a position which offers the least resistance. For example, if the wire-in-tube device was in the position as shown in FIGURE 3, and it was then laterally deflected to an equidistant point on the other side of the phantom line, the new position of the outer tube would now have reversed the curvature of the prestressed inner core wire. The core wire, in seeking to regain its original curvature by virtue of its internal stress, would turn around within the tube until its residual curvature was more nearly in the same plane as the curvature of the tube. This residual force in turning is transmitted as torque to the outer free end of the wire and to anything attached thereto causing it to travel in angular motion. As more fully described in application Ser. No. 203,352, the torque is applied very rapidly thus causing any object attached thereto to snap from one angular position to another. This represents the basic movement of the tube in the novel snap-acting electrical mercury switches hereinafter described. It should be noted that if there were no objects on the free end of the wire, the torque developed by placing a reversed curvature on the tube would cause the wire to turn a full 180 degrees in seeking the position of least resistance following the new curvature of the outer tube.

With reference to FIGURE 1, there is shown an enclosure 23 of glass or other impervious insulating material hermetically sealed and so constructed as to provide a reservoir for two pools 24 and 25 of an electrically conductive liquid metal such as mercury. Associated therewith and affixed to the glass enclosure, are external contact terminals 26 and 27. Perpendicular to the axis of the tubular enclosure there is a metal cup 28 sealed to the enclosure. A thin walled tube 20, as above described, is sealed concentrically around a corresponding opening in the metal cup at the point 30. The opposite end of the tube is sealed closed thus providing a sealed atmosphere within the glass enclosure. A core wire 21 with a preformed curvature thereto is inserted within the tube 20 extending beyond the cup 28 and into the interior of the switch. The wire is integrally connected to the contact bar 32 having downwardly directed arms 33 and 34 on either end. Arm 33 of the bar is continually in contact with pool 24 wit-h the arm 34 being intermittently dipped into pool 25 depending upon whether the switch is open. or closed.

In FIGURE 1 the arm 34 is out of contact with the pool, the switch now being open. If the tube 20 is laterally deflected, a torsional force is exerted on the prestressed curved core wire 21 as above described, thus causing it to rotate through a small angle of rotational movement. The rotation is very fast and thus in essence it snaps the contact arm to the closed position as shown in FIGURE 2. If the tube is subsequently moved in the opposite direction, the contact bar will again pivot about the axis of the tube causing the :arm 34 to snap back out of the pool 25 thus breaking the electrical circuit.

As can be seen in the drawings, the arm 34 is extended well below the surface of pool 25 when the switch is closed. When the switching means is activated, the arm begins its assent from a point below the surface and thus the current carrying capacity of the switch is not immediately affected. When the end of arm 34 reaches the surface of the pool it is travelling at a high rate of speed and thus a clean and fast break is made between the contacts. Thus arcing which often is encountered in mechanical switches and fluctuating current capacities which are encountered in tilting mercury switches are both eliminated. This preaccelerated contact separation is achieved by use of the snap-acting tube which causes the contacts to snap apart upon activation of the switching means.

The glass enclosure may also be extended perpendicular to the axis of the tubular enclosure 23 wherein another tube is aflixed similar to the switch shown in FIGURE 11. With the core wire properly extended and a series of contact bars attached thereto, a switch can be made within the scope of this invention having multiple contacts.

In FIGURE 4 there is shown a modified form of the invention comprising two pools of liquid metal such as mercury 41 and 42 within the glass enclosure 40 with external terminals 43 and 44 associated therewith. The tube 20 extends down and is sealed to metal cap 45 and includes the prestressed core wire 21. Attached to this core wire is a wetta-ble non-insulated displacer 46 which upon deflection of the tube will rotate about the point 47 at the end of wire 21. Movement of the displacer to the phantom position draws the meniscus of one pool over to join the second pool when the edge of the displacer touches the second pool. If the displacer is moved back out of contact with the second pool, the meniscuses break from each other thus breaking the circuit through the switch. If a non-wettable displacer is used with more mercury in the pools, the movement of the displacer to the phantom position would cause the mercury pools to recede from surface tension thereby interrupting electrical contact between them. If it moved back to the position shown in full, the free pool meniscuses would then join thus completing the circuit.

In FIGURE 5 there is shown a similar electrical switch except the axis of the tube 20 is horizontal, the vertical. deflection of which causes the non-wettable insulated displacer block 50 attached to the core wire 21 to pivot the core wire 21 snaps through a small angle of rotationv thus causing the displacer block 50 to move to the position shown in phantom. This displaces the mercury in the pool 53 causing it to spill over into poo152, the two pools forming a lip as indicated in phantom thus completing the circuit. When the tube 20 is deflected in the opposite direction, the displacer 50 is snapped back out of the pool allowing the pools to separate by action of gravity thus breaking the circuit. With the electrical switch constructed in this manner, a more compact unit is obtainable.

The snap-acting tube may also be used in glass switches comprising one pool of liquid metal. In FIGURE 6, a conductive bar 60 is affixed to the core wire of the tube 20 perpendicular to the axis of the tube. The tube extends through a metal cap 61 attached to the glass enclosure 62 having one pool of mercury 63 with an external terminal 64 associated therewith. Opposite the said pool, is another external terminal 65 which is connected to the conductor bar 60 by means of a flexible conductor 66. As the tube 20 is moved from side to side, the inner core wire 21 snaps through angular motion causing bar 60 to dip in and out of the pool thus making and breaking the circuit between the two terminals 64 and 65.

FIGURE 7 represents a modification of the device shown in FIGURE 6, for here a non-Wettable displacement block is snapped into the pool of mercury to break contact between the pool and a solid metal conductor. In this device a bar 70 is aflixed to the core wire of a tube 20 perpendicular to the axis of the tube which tube is sealed to the cap 71 of the glass enclosure 72. At the end of the bar 70, is a ceramic non-wettable displacer 73, suitably in the shape of a cylinder. A solid conductor 74 having an external terminal connection extends down from the top of the glass enclosure into a pool of mercury 75 having terminal 76 associated therewith. The ceramic cylinder 73 is disposed about the base of a conductor 74 at the point where it comes into contact with the pool of metal 75. Due to the surface tension properties of liquid mercury, the movement of the cylinder into the pool will break the electrical connection between the pool and the conductor 74. This is the position as shown in FIGURE 7. When the tube is deflected, the core wire will snap through angular motion thus causing the ceramic cylinder to lift out of the pool as shown in phantom. This again establishes an electrical connection, the pool now being in contact with the solid conductor.

In FIGURE 8 the angular movement of the core wire 21 causes displacer block 81 to move up and down as shown by the arrows. When the block is depressed into the pool '82, the mercury rises to the phantom line thus completing an electrical connection between the two solid conductors 83 and 84. When the block is snapped back out of the pool, the mercury falls and the contact is broken.

A single pool of mercury may also be used to construct a double throw switch as shown in FIGURE 9. A suitable glass enclosure 90 may be constructed having one pool of a conductive liquid metal 91 having a solid conductor 93 in permanent contact therewith. The glass enclosure is hermetically sealed and includes an extension perpendictllar to the axis of the pool of liquid metal through which the inner core wire 21 passes, the tube 20 terminating in sealed relationship with the metal cap 94. Connected perpendicular to the axis of the tube and to the core wire, is a bar having conductive portions 95 and 96 at either end with a nonconductive portion 97 in the middle. The two conductive ends are connected through flexible conductors 98 and 99 to outside terminals 100 and 101. Terminal 102 is connected to permanent conductor 93.

In this type of switch the electrical connection is maintained between the center connections 102 and one of the other two terminals 100 or 101 at any one time. In the drawing the end 95 is in contact with the pool thus creating an electrical connection across terminals 100 and 102. If the tube is deflected, the core wire snaps through an angular rotation, raises end 95 out of contact with the pool and simultaneously depresses end 96 into the same pool, thus making an electrical connection across terminals 102 and 101 while breaking the connection between terminals and 102.

In FIGURE 11 there is shown a multiple contact form of the double throw switch shown in FIGURE 9. A series of contact bars 96 having insulated portions 97' are suitably afiixed to an extension of the core wire 21 which extends through a series of interconnected tubular glass enclosures 90'. Each contact bar is associated with its own pool of liquid metal 91' and thus all of the switches can be' operated simultaneously upon deflection of the tube 20.

In FIGURE 10 there is shown a device which snaps an insulating barrier into and out of a liquid metal pool contacting one solid metal conductor thereby permitting contact between that pool and another liquid metal pool contacting another conductor. In this device a bar is affixed to the core wire 21 of a tube 20 perpendicular to the axis of the tube which tube is sealed to the cap 111 of the glass enclosure 112. At the end of this bar is a ceramic cup-shaped element 113 acting as an insulating barrier which is located concentrically with respect to the solid conductor 114 having an external terminal connection. The pool of liquid metal 115 have external terminal 116 associated therewith. The switch is shown in the closed position as the rim of the ceramic nonwettable cup is lying beneath the surface of the liquid metal pool 115, the liquid metal in the cup this being in contact with the liquid metal in the pool. The solid conductor 114 is always in contact with the liquid metal in the cup. When it is desired to open the switch the torsional responsive tube 20 is deflected in the appropriate direction causing the bar 110 to traverse upwardly through angular motion about the axis of the tube. As explained previously, this will snap the ceramic cup up out of the pool thereby placing the rim of the cup clear of the liquid metal meniscus of the pool 115. The position'of the cup when the switch is open is shown in phantom in the drawing and it now contains a separate pool 117 of liquid metal. While the conductor 114 is in contact with liquid metal within the cup, this small pool 117 is separated from the liquid metal pool 115 in the glass enclosure and thus the contact between the terminals 114 and 116 is broken. A high acceleration rate for the ceramic cup is produced by the snap action eflect of the wire-in-tube device, thus eleminating trail off and arcing as the switch is moved between open and closed positions. It is to be noted that in this embodiment the making and breaking of the contact is made between two pools of liquid metal and not between a solid conductor and a pool of liquid metal.

In all switches, the core wire is suitably insulated so that the tube does not become electrically alive. The tubes are preferably sealed at their outer ends and to the metal caps so that the entire switch enclosures can be hermetically sealed thus providing a constant atmosphere within the switch body. In addition, the hermetic sealing makes the switch explosion-proof thus permitting it to be mounted in hazardous areas without the cumbersome and costly explosion-proof external housings now required for enclosing electrical switches. A simple metal enclosure could be readily furnished for mechanical protection of the glass switch envelope when required.

The metal cap or cup attached to the glass envelope provides a basis for a rigid all metal mounting thus avoiding the clamping of fragile glass parts. Any style of threaded sleeve sheet metal bracket or other mounting can be readily attached. Thus the position of the switch can be rigidly maintained providing easy replacement of the same without requiring any adjustment in the mechanism which deflects the tube to activate the switch.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An electric switch comprising a hermetically sealed enclosure, an elastically deflectable outer tube sealed in the wall of the enclosure and extending both inside the enclosure and outside the enclosure, said tube being sealed adjacent its end outside the enclosure, said end outside the enclosure being deflectable, and said tube having an open end inside the enclosure, a core wire having a preformed linear curvature thereto freely disposed within the interior of said tube and extending through an open end of the tube into the interior of the enclosure, a plurality of contact elements inside the enclosure, at least one of said contact elements consisting of a pool of liquid metal, means operatively connected to the interior end of the core wire, pivoting about the axis of the inner end of the tube, for opening and closing the electrical circuit through said contacts, said means pivoting under snap action between open and closed positions upon deflective actuation of the outer end of the tube.

2. A switch of claim 1, wherein said outer tube is straight in a relaxed position but assumes a curvature when the precurved core wire is placed inside of it.

3. An electrical switch comprising a hermetically sealed enclosure, a pool of liquid metal disposed within said enclosure, a solid conductor in contact with said pool, an elastically defiectable outer tube extending through a Wall of the enclosure and in scalable relationship therewith, a core wire having a preformed curvature thereto freely disposed within the interior of said tube and extending into the interior of the enclosure, a rod integrally connected to said core wire having an electrically conductive portion at either end separated by a non-conductive portion, flexible conductors connected between terminals outside the enclosure and the '8 ends of the rod, said rod pivoting about the axis of the tube and engaging alternatively a conductive end of said rod with the metal pool upon deflective actuation of said tube, thereby closing the electrical circuit between the solid conductor and the terminal associated with that end of the rod.

4. An electrical switch comprising a series of interconnected hermetically sealed enclosures, a pool of liquid metal disposed within each enclosure, a solid conductor in contact with each pool, an elastically deflectable outer tube extending through a wall of an end enclosure and in sealable relationship therewith, a core wire having a preformed curvature thereto freely disposed within the interior of said tube and extending into the interior of the end enclosure and through every other enclosure, a rod for each pool integrally connected to said core wire having an electrically conductive portion at either end separated by a non-conductive portion, flexible conductors connected between terminals outside the enclosures and the ends of each rod, said rods pivoting about the axis of the tube and engaging alternatively a conductive end of the rod with its respective metal pool upon deflective actuation of said tube, thereby simultaneously closing the electrical circuit between the solid conductor and the terminal associated with that end of each rod.

References Cited UNITED STATES PATENTS 1,937,746 12/1933 Cramblet 200--152 2,060,812 11/1936 Gehrand et al. 335-52 2,172,423 9/1939 Wangemann 200-152 2,564,081 8/1951 Schilling 200152 X 2,725,445 11/1955 Bosch 200-144 2,750,466 6/1956 Patterson 200--152 X ROBERT K. SCHAEFFER, Primary Examiner.

R. S. MACON, Examiner.

H. HOHAUSER, Assistant Examiner. 

1. AN ELECTRIC SWITCH COMPRISING A HERMETICALLY SEALED ENCLOSURE, AN ELASTICALLY DEFLECTABLE OUTER TUBE SEALED IN THE WALL OF THE ENCLOSURE AND EXTENDING BOTH INSIDE THE ENCLOSURE AND OUTSIDE THE ENCLOSURE, SAID TUBE BEING SEALED ADJACENT ITS END OUTSIDE THE ENCLOSURE, SAID END OUTSIDE THE ENCLOSURE BEING DEFLECTABLE, AND SAID TUBE HAVING AN OPEN END INSIDE THE ENCLOSURE, A CORE WIRE HAVING A PREFORMED LINEAR CURVATURE THERETO FREELY DISPOSED WITHIN THE INTERIOR OF SAID TUBE AND EXTENDING THROUGH AN OPEN END OF THE TUBE INTO THE INTERIOR OF THE ENCLOSURE, A PLURALITY OF CONTACT ELEMENTS INSIDE THE ENCLOSURE, AT LEAST ONE OF SAID CONTACT ELEMENTS CONSISTING OF A POOL OF LIQUID METAL, MEANS OPERATIVELY CONNECTED TO THE INTERIOR END OF THE CORE WIRE, PIVOTING ABOUT THE AXIS OF THE INNER END OF THE TUBE, FOR OPENING AND CLOSING THE ELECTRICAL CIRCUIT THROUGH SAID CONTACTS, SAID MEANS PIVOTING UNDER SNAP ACTION BETWEEN OPEN AND CLOSED POSITIONS UPON DEFLECTIVE ACTUATION OF THE OUTER END OF THE TUBE. 